Fluid-type support structure for simulating flotation-type support

ABSTRACT

A cushion is constructed with an internal, soft matrix secured to, and contained within, an elastic and flexible envelope within which a fluid is contained at atmospheric pressure. Over the matrix is placed a cover of a material whose surface has a low coefficient of friction. The foregoing produces, when a person sits on the cushion, a substantially uniform pressure which is sufficiently low, and a resistance to lateral movement of the person sitting on the cushion which is also sufficiently low, to prevent or minimize the formation of decubitus ulcers.

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6 mm ne e u l Sm S n mvk Pow m m was r. mmm uhfl 5 5 3 0 5 3 9 4 3 MP S "3 T my N m E M S mm mA rT S D E H N U 6 w 5/347X decubitus ulcers.

I I I I H l ||I Patented April 13, 1971 5,574,873

2 Sheets-Sheet 2 I 4 u I Egy- 10.

FLUID-TYPE SUPPORT STRUCTURE FOR SIMULATING FLOTATION-TYPE SUPPORT BACKGROUND OF THE INVENTION 7 This invention relates to cushions for seats and to pads for beds constructed so as to prevent or minimize the formation of in the construction of support structures, such as seat cushions and bed pads, intended to prevent or minimize the formation of such ulcers.

1 As is known, pressure is defined as weight per unit area. Thus, the smaller the surface supporting a weight, the higher the pressure exerted against the supporting surface. Hence, when supported by the usual supporting surfaces, certain parts of the body, such as the sacrum, the ischael bones of the buttocks, the hips, and the heels, by being prominent, tend to support a relatively large weight per unit area and, thus, the tissue between these bones and the usual supporting surface tends to be under a disproportionately large pressure. In addition, the bony prominences of the body prevent the reduction of such large pressures by not allowing the overlying tissues to move away from the compressing forces so as to conform to the shape of the supporting structure. However, if the supporting structure is made soft enough to be moldable to the contour of the supported part, these localized high pressures on the overlying tissue are reduced and the pressure becomes more evenly distributed. Fluid support, such as that provided by water, is ideal for this purpose and reference is made to two copending applications, Ser. No. 488,202 (filed Sept. I7, 1965) and Ser. No. 659,126 (filed Aug. 8, I967), both filed by myself jointly with others.

Shear is the second effect associated with the formation of decubitus ulcers. Shear is the lateral distortion of skin and subcutaneous tissues which takes place when the supporting surface does not move jointly with, and in response to, lateral movement of the body being supported, the skin and tissues being restrained by frictional resistance between the skin, or the person's clothing, and the supporting surface. When the persons body moves laterally, and the skin is thus restrained, the skin cannot adjust to this movement, because it is not sufficiently elastic, and a distortion of the connecting tissues results. Pathologically vascular occlusion may occur from the distortion of the connecting tissues, because of the stretching, the torsion, or the compression of the blood vessels. At its worst, there may be actual disruption of vascular and tissue elements, with secondary contusion and laceration of the distorted tissues. The well person prevents or compensates for this shearing effect by automatically adjusting his weight as he sits down, placing the supporting skin surface in the proper weight bearing position relative to the center of gravity of the supported body weight. Also, the normal person, by periodically rising slightly to move, releases the lateral pull on his tissues before material damage is done thereto. However, the person whose sensory, or motor function is insufficient to appreciate the value of making these adjustments will be prone to the deleterious elTects of tissue shearing.

BRIEF SUMMARY OF THE INVENTION It is an object of my invention to provide a cushion for a chair or a pad for a bed which will support a person at a uniform, low pressure and which will subject a persons skin and tissues to no shearing forces or minimum amount thereof.

By enclosing a fluid in an elastic and flexible envelope, and by preventing this envelope from locally ballooning out, when weight is applied, by restraining it with an internal matrix, a

fluid support cushion is provided which results in supporting a person at a uniform, relatively low pressure. The internal matrix is very compressible so that it provides little support, yet at the same time it is not readily stretchable, so that it can maintain the shape of the seat. The support is provided by the internal fluid, such as air or water. When air is used it is compressed to the extent that the uniform internal pressure rises to the necessary level to support the body. By being very compressible the internal matrix does not interfere with the uniform pressure and the moldability of the supporting fluid, is easily displaced downward or sideways by the supported body, but by resisting elongation, the internal matrix prevents the person from sinking to the bottom of the cushion.

l have also discovered that by making the cover of the supporting seat slippery, shearing is minimized, i.e., an antishear effect is introduced. By doing this, one is essentially lowering the frictional resistance between the patients skin, or clothing, and the cushions cover, this frictional resistance otherwise tending to exert a lateral distortion on the supporting tissues when body-weight shifting takes place. However, to maximize this antishear effect, the lowest possible pressure should exist between the supporting surface and the overlying tissue, because the amount of frictional resistance is proportional to the pressure of the supported body, as well as the coefficient of friction of the supporting surface. A cushion constructed in accordance with this invention, by providing such low pressures, maximizes this antishear effect.

The cushion has another antishear property inherent in its construction. The fluid supporting medium provides no shear effect which can exert a lateral pull on the overlying tissues. The envelope of the cushion, being easily stretchable, will exert a lateral pull on the tissues only when the forces necessary to stretch it are great enough to exert their effects on the supporting tissues. In other words, the envelope stretches more readily than the tissues are distorted up to some finite point, a point which is not reached in normal usage of the cushion. Toward this end the upper surface portions of the internal matrix, and the envelope portions secured thereto, are capable of relatively unrestricted lateral movement, over a limited distance.

The foregoing and other objects of this invention, the principles of this invention, and the best modes in which I have contemplated applying such principles will more fully appear from the following description and accompanying drawings in illustration thereof.

BRIEF DESCRIPTION OFTHE VIEWS FIG. I is a perspective view of a cushion constructed in accordance with my invention, viewed from the back and one side thereof, showing the internal matrix in dotted lines;

FIG. 2 is a sectional view taken along the line 2-2 in FIG. 1, but at an enlarged scale;

FIG. 3 is a top view of the cushion shown in FIGS. 1 and 2, but portions of the cover and of the envelope are cut away for purposes of illustration, FIG. 3 being at substantially the same scale as FIG. 2;

FIG. 4 is a bottom view of the cushion shown in FIGS. 1, 2 and 3, but at a reduced scale;

FIG. 5 is a greatly enlarged, partial view, showing one of the front comers of the cushion, without the cover, and with the envelope cut away;

FIG. 6 is a partial, sectional view but illustrating a modification of my invention;

FIG. 7 is a partial, elevation view taken along theline 7-7 in FIG. 6;

FIG. 8 is a sectional view of still another modification of my invention;

FIG. 9 is a perspective view of a further modification of my invention illustrating a pad adapted for use on a bed; and

FIG. 10 is a sectional view taken along the line 9-9 in FIG. 8.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, a cushion 10 is provided which may be placed on a chair, not illustrated, or any suitable supporting structure. The cushion comprises a flexible and elastic membrane or envelope l2 surrounding and enclosing an internal means 14 which is readily deformable under compression but which is substantially nonstretchable, the envelope being substantially impermeable to fluids such as air and water.

The internal means 14 is preferably in the form of a matrix or insert and is hereinafter referred to as a matrix." The matrix 14 is formed with horizontal and vertical (FIG. 3) cross channels 16 and 18 extending across the full width and length of the block, but extending only part way down, as best illustrated in FIG. 2. The cross channels 16 and 18 thus define parallel, spaced rows of upstanding, flexible columns or fingers 20 which may be easily compressed and, because of the spaces provided by the channels 16 and 18, may more readily move laterally. The spaces provided by the channels 16 and 18 allow for displacement of the matrix 14 when supporting a body.

The internal matrix 14 is preferably made from a foam material, i.e., an open pore expanded cellular material, that is, one that has communicating cells, and it is preferably an ether-type reticulated polyurethane foam, but other types could be used also, such as latex foams, ester-type polyurethane foams, and vinyl foams. The ether-type polyurethane foams are preferred because of their relatively low weight, economy and manufacturing convenience. The foam material, however, must have a low density i.e., it must be soft and easily compressible so that substantially no, or little, counterforce is exerted by it upon the supported person, whereby the support function is performed substantially entirely by the internal fluid.

A suitable ether-type polyurethane foam is available from the Scott Paper Company. Such a polyurethane foam is described in US. Pat..No. 3,l7l,820, issued to R. A. Volz, in which the foam is formed by a flexible three-dimensional network of interconnecting strands and nexus of a polyester polyurethane resin whose strands and nexus are integrally interconnected at spaced-apart points so as to form the isotropic skeletal outline of a multitude of polyhedrons whose faces are polygonal which are common to a polyhedron adjacent thereto and are open and substantially free from membraneous polyurethane resin.

The columns 20 have a uniform cross section and are evenly spaced, as shown, but the top surface of the matrix 14 slopes uniformly, from back to front, the back of the cushion being thicker than the front thereof, so that the top surface 22 of each column 20 is a sloping surface.

The envelope 12 is bonded, by a suitable adhesive, such as a natural latex adhesive, to the sloping top surfaces 22 of the columns 20, to the four outer sides 26 of the matrix 14, and to the flat bottom surface 28 of the matrix. The four sides 26 of the matrix 14 are formed by the exposed sides of the peripheral columns and the periphery of the base 30, the columns 20 and base 30 being integral.

The columns 20 should be long enough so that when the patient is seated on the cushion, the columns 20 will not be fully compressed. The reason for this is that if the columns 20 are fully compressed, counterforces will be produced tending to support the body, the counterforces becoming localized under the prominent parts of the body. This is undesirable, since the desired uniform pressure distribution would no longer exist. Also, if the columns 20 are fully compressed, the patient will in essence have bottomed out, he will then be supported on the firm mass of compressed matrix at the bottom of the cushion instead of being supported by the fluid. Further, if the columns are fully compressed their ability to permit their upper surface portions, and the envelope portions secured thereto, to move laterally, over a limited distance, will be substantially reduced or eliminated. Preferably the channels near the front of the seat extend farthest down, to the line A-A in FIG. 2, but the remainder do not extend as far down, as shown.

Since substantial lateral movement of the columns 20 is contemplated, the cross section of the columns 20 must be large enough so that they will not readily fracture because of the repeated lateral movements.

To minimize the shear forces on the patient, a cover 35, having smooth and slippery surfaces, is placed over the top section 32 of the envelope 12, the cover 35 extending down the sides of the envelope and being fitted over the bottom of the envelope along bottom, peripheral portions thereof. The cover 35 is preferably formed from a nylon tricot material, although a polyethylene plastic material of about 0.004 inch thick has also been found suitable for the cover 35.

The upstanding columns 20, being secured to the surface defining the top section 32 of the envelope 12, provide stability to the envelope. That is, as one sits on the cushion, the fluid within the cushion will be displaced, but the columns 20, being secured to the envelope, prevent it from ballooning outward and minimize the bulging or pushing out of the envelope as the fluid is displaced, thus stabilizing the envelope.

in the preferred embodiment, the envelope is sealed so as to contain within it air at atmospheric pressure. While the use of air within the cushion at atmospheric pressure is preferred, if a partial vacuum is provided within the envelope, the patient would sink into the cushion a greater extent than if atmospheric pressure is contained therein. The use of a partial vacuum would result in more surface area molding about the patient, and would tend to provide support at a still lower unit pressure, but the height of the columns would have to be increased accordingly.

The envelope or membrane 12 is preferably made from' a latex sheet material, such as dental-dam sheet rubber. This type of envelope has been found to be satisfactory if its thickness is about 0.008 inch, and if the material can be stretched so that it is at least 500 percent larger than its normal unstretched size without fatiguing the material.

At least the top section 32 of the envelope must be sufficiently flexible and elastic so that it will stretch and permit the supported body to sink down into the fluid until the body is supported by the fluid and not by the envelope. If the section 32 of the envelope 12 is not flexible and elastic to this extent, local portions of the envelope will be tensioned and they will support the body, resulting in localized, high pressure areas which are undesirable.

Since the cushion has a uniform internal pressure and a flexible and elastic envelope which tends to push out where there is no load being supported by it, or a lesser load, it is desirable to counteract this tendency by making the cushion of wedged shape, that is, thicker at the back, where the greater load is imposed upon the cushion, and thinner in the front, where the lesser load is placed.

In one embodiment the matrix 14 has a flat bottom surface 28 and a sloping top surface 22, the four outer sides 26 of the matrix being vertical, as illustrated in FIGS. 2 and 3. The back part of the matrix is approximately 2%inches high and the matrix tapers down to a front part of about 1% inches high. The matrix 14 is approximately 16%inches wide and about 15%inches deep and is divided by seven parallel vertical channels 18 into eight vertical rows and by seven parallel, horizontal rows into eight horizontal rows, each channel being about A inches wide. The channels extend downwardly to about rinch from the bottom surface of the matrix.

To further control the tendency of the sides of the cushion to balloon outwardly, a frame, not illustrated, may be added to the cushion, around the sides thereof, the frame being made of a suitably rigid material.

The bottom surface 28 of the matrix 14 may be coated by a suitable material for the purpose of fluid sealing the surface. in this event, the envelope 12 may be secured to the peripheral surfaces of the bottom surface 28, instead of extending across the entire bottom surface 28.

A rigid sheeted member, such as a suitable plastic, could be bonded to the bottom surface 28 of the matrix and the envelope 12 could be secured only to the peripheral portions thereof without extending across the entire bottom surface 28, but this is not illustrated.

Instead of using a top section 32 which is flexible and elastic, it would be possible to use a sheeted material without this elasticity, if enough material is provided so that it would be flaccid at all times, whereby as a person sits on the cushion there would be enough material to mold to the contour of the person without tensioning the material.

Some patients have found that a cushion constructed in accordance with this invention and containing air only to be hot after sitting on it for a period oftime. To make the cushion more comfortable for such patients, the cushion may be filled partly or completely with a liquid, such as water. I prefer to fill of the cushions volume with water and to have the remaining /6; as air at atmospheric pressure. Since the matrix is relatively inelastic, a stiffer cushion results when it is filled completely with water.

As illustrated by the partial illustrations of FIGS. 6 and 7, a cushion 59 is provided with a valve 60. The valve 60 is secured to the envelope 62 at the rear of the cushion and communicates with a cavity 64 which extends toward the cross channel 66 so that water may be more easily placed within the envelope. Preferably, the envelope is filled with enough water so that when the cushion is compressed by the weight of a body upon it, at least a portion of the lower surface of the upper wall of the envelope will contact the water.

Another means for conducting body heat away from the cushion would be to provide a cover, not illustrated, to be placed over the envelope 62 and made of a sufficiently flexible metal, such as a thin sheeted or woven aluminum cover. The cover could also bemade of thin strips of metal bonded to strips of flexible and elastic sheeted membrane, such as the dentaI'dam-sheeted rubber, the thin sections of metal and rubber alternating along the cover. Also, such a cover could be provided by weaving metal and elastic threads.

For use with other patients, it is sometimes desired that the cushion be warm and in such instances a warm liquid, such as water, may be placed within the envelope 62, orcirculated therein by connections thereto and apparatus not illustrated.

Also, referring to FIG. 8, it has been found that if a second or outer cover 37 of the same or similar material as that of the first cover 35, is placed over the cover 35, and secured only at the bottom of the cushion, the outer cover 37 will slide freely on the inner cover 35 and further reduce the shear forces on the patients body. This is so because when only one cover is used, the slip between the patient (or the patients clothes) and the single cover is not so great as the slip between the opposed, contacting surfaces of the two covers. When the two-cover construction is used the patient may at times move together with the outer cover relative to the inner cover because the coefficient of friction will usually be lower between the surfaces of the covers, than between the patient and the outer cover.

It will be noted that a matrix or insert 39 illustrated in FIG. 8

does not have laterally movable columns. By making the insert 39 sufiiciently soft and with enough lateral compressibility I and elasticity to provide some lateral movement of its component portions, the support function will be provided by the fluid contained within the cushion or pad, instead of by the insert. Thus, as the body, or portions thereof, sinks into the cushion or pad the envelope will mold about the contours of the supported body, or portions thereof, and the bodys weight will be distributed over a large surface area, resulting in low unit pressures. This will also tend to simulate the flotation provided by a body floating on a liquid.

Referring to FIGS. 9 and 10, the invention is incorporated J in a pad 76 for use on a bed, or like structure. The pad 76 is placed in an opening 78 formed in a block 80. .The pad 76 and the block 80 are both placed preferably upon an ordinary -mattress 82 of a bed. The pad 76 is surrounded by portions of the block 80, as illustrated in FIG. 9. Over the pad 76 and over the block 80 is placed a cover 84 of slippery material.

The pad 76 is constructed similar to the cushion 10 described in connection with FIGS. 1 to 5, being provided with an internal matrix 90 with columns similar to those described in connection with FIGS. 1 to 5 except that the matrix 90, and thus the pad 76, has a uniform thickness which is approximately the same as the thickness of the block 80. However, it will be understood that the block 80 could be made thicker than the pad 76 in which case the opening 78 in the block would be equal to the thickness of the pad only, and in which case the pad would then rest on a part of the block and not directly on the mattress as illustrated in FIG. 10. The pad 76 is enclosed by an envelope 86 to contain a fluid which may be air exclusively or it may contain air and water, or water exclusively, as desired. Also, the pad 76 may or may not have its own slippery cover, no such cover being illustrated in FIG. 10.

The block 80 is made of suitable foam material, preferably a very soft foam material, as it can thus provide a low-pressure support to the peripheral body areas which, being relatively lighter, do not require the support necessary to hold the trunk and the peripheral parts are less likely to compress this foam. A slippery cover 84 for the entire unit provides generalized antishear effect, and the cover 84 may be tucked under the block 80, as shown.

In any of the foregoing embodiments, the use of water has certain advantages, since it is relatively economical, but even though the envelope is substantially impervious, after a period of time, the water tends to evaporate through the envelope, requiring periodic replacement. To overcome this disadvantage a viscous material, such as a urethane liquid may be used. Another possibility would be to use glycerine instead of water.

In summary, to provide a structure for the therapeutic support of a patient it is desirable to simulate the low surface pressures which are produced when the patient is floated on a liquid. This is simulated by a support structure comprising a flexible and elastic envelope containing a fluid which may be air, water, or air and water, or some other fluid. The unloaded or lesser loaded parts of the top section of the envelope are restrained from excessively ballooning outwardly, as the weight of the patient is placed on the top section of the envelope, as the envefope molds about the contours of the body, by the internal matrix or insert, the matrix or insert, however, being soft enough to provide virtually no support function, or a minimum support function, and the support structure being deep enough and having a high enough, initial (unloaded) internal pressure so that the patient does not strike bottom when resting upon the structure.

Also, it is desirable to eliminate, or reduce to a minimum, shear forces on the patient and this is accomplished by providing the support structure with one or more of the following features: a cover providing sufficient slip between the patient and the seat, a flexible and elastic envelope, a soft and easily compressible insert secured to the bottom and top sections of the envelope, and the insert having upstanding columns readily movable laterally.

From the foregoing it is seen that I have provided a fluidtype support structure for simulating flotation-type support of a body, or a portion thereof. Without intending to be all inclusive, several distinct advantages are to be noted. For instance, when the cushion or pad heretofore described contains air, a much lighter structure results than if an envelope containing water, without any internal insert or matrix, is used. Also, the internal insert or matrix makes an enclosed space, said upper wall being constructed of a flexible and elastic dental-dam sheet-rubber material, means disposed within said envelope, said means being readily deformable under compression but being substantially nonstretchable, said means defining a plurality of interconnected passageways, a fluid disposed within said envelope and generally throughout the passageways in said means, said fluid having a pressure sufficient to support the major portion of the weight of a portion of a body disposed on said upper wall when said means is partially compressed, portions of said upper wall of said envelope being secured at least at spaced points to said means, whereby separation of said portions of said envelope from said means is substantially prevented when the fluid pressure is increased due to the weight of a portion of a body disposed on said upper wall, and at least the portion of said means beneath said upper wall being of a nature permitting, over a limited distance, relatively unrestricted lateral movement of the portion of said upper 5. The structure recited in claim 4 wherein said upper wall has an upper surface which is slippery to further reduce the shear forces on the supported body,

6. A cushion according to claim 5, wherein at least a portion of said fluid is a liquid, said liquid being sufficient in amount to contact at least a portion of the lower surface of said upper wall upon compression of said means when a portion of a body is disposed on said upper wall.

7. A cushion according to claim 6, and a cover over at least a portion of the upper surface of said upper wall said cover being formed from a material which is slippery relative to the material of said upper wall to increase the lubricity of the uppermost surface of the cushion. 

1. A cushion for supporting portions of a body, comprising a fluid-impervious envelope having an upper wall and a lower wall peripherally interconnected to one another so as to define an enclosed space, said upper wall being constructed of a flexible and elastic dental-dam sheet-rubber material, means disposed within said envelope, said means being readily deformable under compression but being substantially nonstretchable, said means defining a plurality of interconnected passageways, a fluid disposed within said envelope and generally throughout the passageways in said means, said fluid having a pressure sufficient to support the major portion of the weight of a portion of a body disposed on said upper wall when said means is partially compressed, portions of said upper wall of said envelope being secured at least at spaced points to said means, whereby separation of said portions of said envelope from said means is substantially prevented when the fluid pressure is increased due to the weight of a portion of a body disposed on said upper wall, and at least the portion of said means beneath said upper wall being of a nature permitting, over a limited distance, relatively unrestricted lateral movement of the portion of said upper wall secured thereto.
 2. A cushion according to claim 1, wherein said means is a matrix having a plurality of channels cut into its surface beneath said upper wall in a manner leaving a plurality of spaced upstanding columns extending from a common base and supporting at least a portion of said upper wall, the upper ends of said columns being capable of relatively unrestricted lateral movement over a limited distance relative to one another.
 3. A cushion according to claim 1, including a support member having an opening therein adapted to receive said fluid-impervious envelope containing said fluid and said means, said support member being adapted to peripherally surround said envelope and to provide support for portions of a body extending beyond the limits of the upper wall of said fluid-impervious envelope.
 4. The structure recited in claim 3 wherein said upper wall is bonded to the upper surface of said columns.
 5. The structure recited in claim 4 wherein said upper wall has an upper surface which is slippery to further reduce the shear forces on the supported body.
 6. A cushion according to claim 5, Wherein at least a portion of said fluid is a liquid, said liquid being sufficient in amount to contact at least a portion of the lower surface of said upper wall upon compression of said means when a portion of a body is disposed on said upper wall.
 7. A cushion according to claim 6, and a cover over at least a portion of the upper surface of said upper wall said cover being formed from a material which is slippery relative to the material of said upper wall to increase the lubricity of the uppermost surface of the cushion. 